An engine control unit or an “ECU” is a widely used type of electronic controller that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by reading values of a multitude of sensors in the engine bay and interpreting the data it receives using lookup tables which adjust engine actuators appropriately.
The ECU monitors various sensors on the automobile such as sensors for oxygen level, coolant temperature, mass air flow, air intake temperature, crank shaft angle, throttle position, cam shaft angle and engine knock. Lookup tables provide feedback information for adjustment and control of ignition timing, cam shaft position, fuel injector input, fuel pump input, fuel pump pressure, cooling fan speed, admission control systems, forced air induction controls, traction controls and transmission gear selections. In many situations, ECUs also send error codes to the vehicle dashboard to indicate immediate problems, such as overheating, or maintenance requirements, like oil changes. In some cases, the error codes activate warning lights which must be deactivated by the dealer.
Certain classes of ECUs are programmable. Modern ECUs incorporate a microprocessor which can process inputs from engine sensors in real time. The microprocessor stores its programming in firmware which is resident in flash memory or e-proms attached to the CPU of the microprocessor.
Programmable ECUs are required, for example, where significant aftermarket performance enhancing modifications have been made. Such modifications often include the addition of a turbo charger, intercooler or modified exhaust system. Programmable ECU's are also used for several vehicle systems, such as engine control module (ECM), transmission control module (TCM), body control module, anti-lock brake system (ABS), airbag control module, and so on, that each receive routine updates from the manufacturer of the vehicle. Each ECU is remapped or reprogrammed to adapt the performance of the involved system to match the required modifications and/or to update the software and parameters of the ECU. Other changes for high performance engines which can be remapped in an ECU include ignition timing, maximum RPM, water temperature correction, transient fueling, low fuel pressure modifiers and a closed loop lambda (in order to modify a target air/fuel ratio), turbo charger waste gate control, staged fuel injection, variable cam timing, gear control and turbo charger anti-lag.